Putrescine, spermidine, and spermine are major polybasic compounds that are found in all living cells. Work from this and other laboratories have shown that these amines are important for many systems related to growth and differentiation. Our studies are directed towards learning more about how these polyamines are synthesized, how their biosynthesis and degradation are regulated, their physiological functions, and the mechanisms of their actions in vivo. Our present studies have concentrated on the biochemistry, regulation, and genetics of these amines in saccharomyces cerevisiae. For this purpose we have used null mutants of this organism that we have constructed in the various biosynthetic pathways. These mutants are not able to make the polyamines and, therefore, are very useful tools for these physiological studies. Work with these mutants have shown a number of interesting and important in vivo functions for the polyamines. In particular, our work has indicated that polyamines are required for growth, for sporulation, for maintenance of the killer dsRNA virus, for protection against oxidative damage, for protection against elevated temperatures, for fidelity of protein biosynthesis, and for the stability of ribosomes and of the ribosome- aminoacytRNA-mRNA complex. Our work during the past year has shown that the different polyamines have different effects and that the requirement for spermidine could not be replaced by putrescine or spermine.